1. Field of the Invention
The present invention relates to a medical device for injecting liquid.
An application for such a device can lie, for example, with a pump used for injecting contrast liquid for medical imaging.
2. Discussion of Related Art
A major problem that results from injecting liquid into patients lies in the risk of the injection device being contaminated by the patient. When a liquid is administered to a patient, there is a risk of the injected liquid flowing back after it has already come into contact with the patient. Also, in the absence of injection, there still exists a risk of contamination by contaminating agents, such as germs, migrating from the patient to the injection device. As a general rule, this situation makes it essential, when treating a new patient, to change all of the portions of the device that have already been used.
There exist several devices in the prior art for reducing the risk of such backflow: EP-A-64853 in the name of MEDEX S. A. describes an injection unit that includes a non-return valve, for example. EP-A-279028 in the names of KABI PHARMACIA GmbH and PFRIMMER-VIGGO GmbH claims a liquid injection device having a non-return valve characterized by the fact that the opening pressure can be set to either of two positions.
Although prior art devices do indeed reduce the risk of backflow, there still remains the risk of the non-return valve leaking. This risk is particularly high in the absence of injection.